Giraffes have elastic blood vessels in their necks, this makes it possible for them to drink water from a pond, without fainting. A giraffe's heart has the formidable task of pumping blood at high enough pressure so that it can flow up the giraffe's neck to the brain. To accomplish this, a giraffe's heart is specially adapted; it generates twice the blood pressure of other large mammals. Having enough blood pressure to pump blood to the brain when the giraffe's neck is extended upward is one challenge, but when the animal lowers its head it risks injury due to excessive blood pressure. To counter this, giraffes are equipped with a pressure-regulating system known as the rete mirabile which restricts the amount of blood that rushes towards the brain when the giraffe lowers its head.
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